Abstract: A coil apparatus for the use of a switching power supply circuit has been found. The coil apparatus having two overlapped coil bobbins has an improved winding arrangement. This arrangement is such that one (P.sub.1) of primary windings which are provided for an inner bobbin are divided into two windings (P.sub.11, P.sub.12) which are electrically coupled with each other, and remaining primary windings (P.sub.2) are sandwiched between the two divided windings (P.sub.11, P.sub.12).

Abstract: An improved structure of a coil bobbin for a transformer in a switching power supply circuit. The coil bobbin comprises an outer bobbin (30) having a first hollow cylindrical member (12) having a first flange (13) located around one end thereof, said first flange having a first terminal plate (15) with a plurality of a first terminal pins (16) and a first grooves (26) for accommodating lead wires, the first member (12) having a second flange (31) located around the other end thereof, and an inner bobbin (2) having a second hollow cylindrical member (21) having a third flange (22) located around one end thereof, the third flange having a second terminal plate (23) with a plurality of a second terminal pins (24) and a second grooves (25) for accommodating lead wires. The coil bobbin in assembled by inserting the second hollow member (21) into the first hollow member (12) so that the first and second terminal plates are parallel with each other in the horizontal direction.